Reaction product of zinc oxide and aldonic acids



United States Patent REACTION PRODUCT OF ZINC OXIDE AND ALDONIC ACIDSAllan E. Chester, Highland Park, Ill., assignor to Poor & Company,Chicago, 111., a corporation of Delaware No Drawing. Application August19, 1950, Serial No. 180,500

2 Claims. (Cl. 260-429) This invention relates to new and useful organiccompounds and more particularly to the reaction products of aldonicacids with zinc oxide and to a method for the preparation thereof.

This application is a continuation-in-part of my copending application,Serial No. 34,127, filed June 19, 1948, which matured into United StatesPatent 2,576,997.

It is an object of the invention to produce water soluble organiccompounds which are substantially free from impurities.

Another object of the invention is to produce new and useful reactionproducts of zinc oxide andaldonic acids. A further object of theinvention is the provision of a new and improved method for preparingcompounds of the type referred to above.

Other objects and advantages of the invention will appear in thefollowing disclosure.

In accordance with the invention it has been found that new and usefulproducts are obtained by reacting zinc oxide with aldonic acids. Thepreferred products are acid soluble and are suitable for use in a numberof ways, especially in electroplating baths and particularly in acidzinc electroplating baths. The preferred use of the products inelectroplating baths is more fully described in my above-identifiedcopending application.

The aldonic acids employed in this invention are derived from aldosesugars by oxidation thereof. A number of suitable aldonic acids areknown, e. g., gluconic, mannonic, galactonic and arabonic acids. All ofthe aldonic acids exist in alpha and beta lactone forms. Gluconic acidis preferred for the practice of this invention because it is morecheaply and readily available than the other aldonic acids. Theinvention is not, however, limited to the use of gluconic acid.

The gluconic acid employed in the practice of the invention exists inseveral forms and the invention contemplates the use of one or more ofthese forms or mixtures thereof including mixtures of the lactone forms.Commercial gluconic acid is available as a 50% aqueous solution ofapproximately 99% gluconic acid and 1% glucose. The presence of theglucose is undesirable because it tends to build up in a plating bathand thereby cause gumminess and stickiness in the bath.

The zinc gluconate prepared according to this invention is substantiallyfree of glucose. It is prepared by heating a commercial 50% gluconicacidsolution to about 120 F. for a time sufiiciently long to melt anycrystalline lactone that might be present. Then one mole of lead freezinc oxide is added for every two moles of gluconic acid present. Themixture is heated to 170 F. with agitation and held for ten minutes oruntil solution of the ingredients is complete. The resultant product iscooled to 120 F. in the liquid phase and poured into large stonewareves- 2,701,811 Patented Feb. 8, 1955 sels and cooled until a waxy solidforms along with some supernatant liquor. The liquor is mainly glucoseand water and is removed from the solid by filtration. The residue isplaced in drying trays where it may be washed with ice water to removetraces of residual glucose. The product is then dried by heating attemperatures below 250 F. until it becomes dry and hard, after which itis ground in a hammer mill or other suitable means. The resultantproduct is stable and non-sticky.

The foregoing description of the preparation of zinc gluconate isadaptable to the preparation of zinc aldonates in general by heatingtogether one mole of zinc oxide with approximately two moles of any ofthe aldonic acids.

The zinc aldonate reaction product may be added to acid zincelectroplating baths according to the method outlined in my previouslyidentified copending application in small amounts to effect aconsiderable increase in the brightness of the electroplated zinc plate.No further chemical treatment of the plates is necessary to bring outthe brightness thereof. The reaction product also has it ptilronouncedanti-burn efiect when added to zinc plating a ts.

It should be noted that glucose, when added alone to acid zinc platingbaths, will not produce bright zinc plates. Glucose or other aldosestherefore are in no sense the equivalent of gluconic or other aldonicacids or the reaction products thereof with zinc oxide for the purposeof the present invention.

The invention is hereby claimed as follows:

1. A process of preparing an acid soluble zinc gluconate which comprisesheating a 50% by weight aqueous solution of approximately 99% gluconicacid and 1% glucose to a temperature of about F. for a time sutficientlylong to melt any crystalline lactone, then adding to said solution onemole of lead free zinc oxide for every two moles of gluconic acidpresent in the solution, heating the resultant mixture to F. withagitation until solution of the added ingredients is complete, coolingthe resultant product to about 120 F. in the liquid phase, pouring theresultant liquid into vessels and further cooling until a waxy solidforms along with some supernatant liquor, removing the supernatantliquor, washing the residual solid with water and drying the washedsolid product at temperatures below 250 F.

2. A process of preparing an acid soluble zinc gluconate which comprisesheating an aqueous solution of gluconic acid containing minor amounts ofglucose to a temperature and for a time sufiiciently long to melt anycrystalline lactone, then adding to said solution approximately one moleof lead free zinc oxide for every two moles of gluconic acid present inthe solution, heating the resultant mixture with agitation untilsolution of the added ingredients is complete, cooling the resultantproduct in the liquod phase, pouring the resultant liquid into vessels,further cooling until a waxy solid forms along with some supernatantliquor, removing the supernatant liquor and drying the solid product.

Ben, vol. 49, pages 720-21, J our. of Chem. Soc. (London), 1880, pages795-6.

Beilstein, vol. 3, 4th edition, 1921, page 544.

2. A PROCESS OF PREPARING AN ACID SOLUBLE ZINC GLUCONATE WHICH COMPRISESHEATING AN AQUEOUS SOLUTION OF GLUCONIC ACID CONTAINING MINOR AMOUNTS OFGLUCOSE TO A TEMPERATURE AND FOR A TIME SUFFICIENTLY LONG TO MELT ANYCRYSTALLINE LACTONE, THEN ADDING TO SAID SOLUTION APPROXIMATELY ONE MOLEOF LEAD FREE ZINC OXIDE FOR EVERY TWO MOLES OF GLUCONIC ACID PRESENT INTHE SOLUTION, HEATING THE RESULTANT MIXTURE WITH AGITATION UNTILSOLUTION OF THE ADDED INGREDIENTS IS COMPLETE, COOLING THE RESULTANTPRODUCT IN THE LIQUOD PHASE, POURING THE RESULTANT LIQUID INTO VESSELS,FURTHER COOLING UNTIL A WAXY SOLID FORMS ALONG WITH SOME SUPERNATANTLIQUOR, REMOVING THE SUPERNATANT LIQUOR AND DRYING THE SOLID PRODUCT.